Doctrine is basically a teaching or belief concerning theological themes. For instance the doctrine of the trinity is the teaching that There is one God, but He manifests Himself as three distinct persons, God the Father, God the Son (Jesus) and God the Holy Spirit.
Till I come, give attendance to reading, to exhortation, to doctrine. - 1Timothy 4:13 Scripture tells us to give attendance, or to pay attention, and to use (Biblical) doctrine. The teachings of the Bible are relevant to life and should be studied.
That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive; - Ephesians 4:14 We should be grounded, or well studied, in the doctrines of scripture. We are not just to accept what we are told or taught but we are to search the scriptures and to study to see if these things are so. As we ground ourselves in the truth of God's word, it will be easier to recognize and to withstand false doctrines. Note that sometimes false doctrines are spread deliberately, and sometimes they are spread unknowingly.
As I besought thee to abide still at Ephesus, when I went into Macedonia, that thou mightest charge some that they teach no other doctrine, - 1Timothy 1:3 There is much teaching in this world that is not of God. We are told that we are not to propagate these false teachings.
But speak thou the things which become sound doctrine: - Titus 2:1 It seems that God wants us to realize that we represent Him and we are to share the truth of His Word with others. Note that the word 'become' in this verse means "to be suitable or proper". We are to speak things that are suitable and proper in the light of God's Word.